Method of flattening flexible sheets faced with wood



16, 1932. A. ELMENDORF 1,871,447

METHOD 0F FLTTENING FLEXIBLE SHEETS FAGED WITH WOOD Filed May 16.' 1931 Patented Aug. 16, 1932 UNITED STATES PATENTiOFFICE- ABHIN ELHENDOBF, OF CHICAGO, ILLINOIS, ABABIGNOR TO THE FLEXWOOD 60mm,

- A CORPORATION OF DELAWARE METHOD OF FLATTENING FLEXIBLE SHEETS FACE!) WITH WOOD Application led lay 16, 1931. Serial No. 537,803.

While the principal shrinkage of wood is across the grain, there is some shrinkage in the direction of the grain as the wood dries from the green state. This shrinkage in the lengthwise direction is not always uniform throughout a given piece of wood; the result being that, in the case of thin veneers, the unequal shrinkage lengthwise of the ain often produces what are known as coc les, namely, bulges in areas where there has been less shrinkage than in the surrounding wood. Therefore, after drying, veneers in which this unbalanced longitudinal shrinkage occurs will not present smooth, flat surfaces; this being true even though the wood be disrupted along the lines of the grain to divide it into numerous closely spaced connected filaments; nor will the bulges or cockles be prevented by gluing the veneer to a fiexible backing. This characteristic of veneer is not objectionable when the veneer can be glued to a rigid supporting surface under pressure, but it is highly objectionable in the case of thin veneers glued to paper, fabric, or other flexible backings and adapted to be cemented or pasted upon a wall or other surface without the employment of means to produce and maintain for a considerable time a pressure that will Hatten out the veneer; the result being that, when the composite sheet, composed of the -veneer and its iiexible backingis pasted to a wall or other supporting surface, even though -it be rolled flat to reduce the cockles, the latter will immediately form again and pull the backing loose from the supporting surface, so that the composite sheet will appear to have blisters therein. This objectionable characteristic of wood veneer is encountered to such an extent that, in the commercial manufacture of iiexible composite sheets composed of thin veneers and paper or fabric backings, as much as 20% of commercial Veneers of some woods that are obtained for the manufacture of this product must be discarded. Thus, there is not only the waste of veneer, but the loss of time in inspecting each lot of veneers and` culling out those sheets that are not satisfactory.

The object of the present invention is to make it possible, in a simple and inexpensive manner, to avoid the aforementioned objectionable consequences resulting from the tendency of some thin veneers to form surface irregularities or cockles due to unequal shrinka e in the direction of the grain, whereby flexile composite sheets, each composed of wood veneer and a backing, ma safely be made of veneer subject to cockles without danger that `the sheets will fail to remain fiat after having been pasted or cemented to a wall or other surface.

I have found that, if thin dry cockled veneer is flattened out and moderately heated the pressure and the heat being maintained for a short time, the cockles will disappear; this being particularly true in the case of veneer glued t'o a flexible backing. If a composite flexible sheet, of which one element is a piece of veneer which has been thus treated, is pasted to a wall, for example, it will remain flat and will'notv thereafter present the appearance of containing blisters. Therefore, in the manufacture of flexible veneerfaced Wallcoverings, or the like,` composed of wood veneer backed with paper, cloth, or other suitable flexible material, I first produce the composite sheet in the usual way, and then treat the composite' sheet to remove the cockles in the veneer, pressing it between hot plates, causing the temperature of the sheet to be raised to about the boiling point of water, and maintaining the temperature and pressure until the desired results are secured; this requiring only a short period of time which ordlnarily will be anywhere from one minute to ten minutes. When the composite sheets are treated in this manner, the need for culling out those sheets of veneer in which cockles are formed is obviated, and, since the cost of the additional treatment is much less than the waste resulting from the discarding of a considerable percentage of the veneers, iiexible composite sheets, one face of which is wood veneer, may be manufactured more cheaply than heretofore.

The various features of novelty whereby my invention is characterized will hereinafter be pointed out with particularity in the claims; but, for a full understanding of my 100 3" Figure -1 is a section through a flexible sheet composedof wood veneer and a backing cemented thereto, showing an irregularity due to unequal shrinkage of the veneer ln-the .d1- rection of the gram, the thicknesses belng greatly exag erated; Fig. 2 is a section on line 2-2 of ig. 1; Fig. 3 is a section taken at right angles to the plane of a composite sheet positioned between two hot plates, the thicknesses of the elements making up the composite sheet being greatly exaggerated;

- have blisters.

Fig. 4 is a perspective v1ew of a fra ent of a panel that has been treated, illustrating the flatness of the surface; and Fig. 5 is a more or less diagrammatic view, illustrating a sheet N being passed betwen a roller and a concave steam chest in the manner of a piece of laundry going through an ironing machine.

Referring to Figs. 1 and 2 of the drawing, 1 represents a sheet of thin wood veneer gluedto a flexible backing 2 of cloth, paper or other suitable material. The thicknesses are greatly exaggerated-in the drawing, as

runs parallel with the plane of the section on which Fig. 1 is taken and at right angles to the plane on which Fig. 2 is taken, unequal shrinkage of the veneer lengthwise of the grain often produces little raised areas or bulges, as indicated at 3. It will be seen that, if these bulges are not reduced, a sheet containing them, when pasted on a wall in the manner of wall paper, willappear to l Even though the bulges or cockles be rolled fiat, they will form again, pulling the backing away from the wall.

These bulges or cockles can be flattened out, and, if the veneer be heated while they are in a flattened condition, the fiber or wood structure will take a set and afterwards remain flat. The degree of pressure employed is not important, except that it should be suicient completely to flatten out the bulges.

' Also, if the pressure be too great, the wood may have a polished and compressed appearance that may be'undesirable. L I have foundA that ordinarily a pressure of about fifty pounds per square inch gives satisfactory `re sults. There are limits to the temperature to which the wood, or rather the composite sheet, may be brought. If the temperature be too low, there will not be the permanent setting of the reduced bulges in a fiat state. If the temperature is too high, there will be, first,

a deterioration of the glue joint, and, second, damage to the wood. I have found that a temperature in the neighborhood of the boil- 05 ing point of water gives the best results,

ferent thicknesses of veneers. Sometimes the` vtreatment may be completed in about a minute, whereas at other times it mayV take ten minutes.

One manner of applying the heat and pressure is illustrated in Fig. 3 in which there are upper and lower hot plates A and B between which the composite sheet is laid. If desired, the composite sheet may be slowly passed through a rotary ironing machine, as indicated in Fig. 5, wherein. X represents the sheet, C represents a stationary curved steam chest, and D represents a. slowly rotating roller. One end of the sheet is inserted between the chest and the roller, so that the sheet is gradually drawn through the machine, each portion thereof remaining under pressure between the chest and the roller for a sufficient length 0f time to effect the intended result.4

After the sheet has been treated in the manner illustrated in Fig. 3 and Fig. 5, it hasthe appearance of a fragment shown in Fig. 4, the surface thereof being entirely fiat. The heating of the veneer softens the same so that the structure thereof readjusts itself,

mean veneer which in commerce is knownv as dry veneer. In other words, my process 1s 1n no sense one whose purpose is to reduce the moisture. content of wood as are ordinary drying processes, but one which operates on a composite product, the veneer element of which has been dried previously.

I claim:

l1. The method of eliminating bulges in dry, thin wood veneer due to unequal shrinkage in the direction of the grain in drying from a green state, which consists in pressing the veneer flat, heating the veneer to a temperature in the neighborhood of the boiling point of water, and maintaining thel pressur?i and the heat until the wood has softene 2. The method of flattening a flexible composite sheet composed of a flexible backing glued to thin wood veneer having therein bulges due to unequal shrinkage in the direction of the grain in drying from a green state, which consists in pressing the sheet fiat, heating it to a temperature in the neighborhood of the boiling point of water, and maintaining the pressure and the heat until the wood has softened.

3. The method of insuring flatness of surface in a composite sheet composed of thin wood veneer glued to a exible backing and I ruptured along the grain into many connected filaments, where the wood is of a t in which bnlges result from uneven shr1 age in the direction of the grain in drying from a green state, which consists in pressing the sheet fiat to reduce the bulges and heating t suiciently to soften the wood while held 4. The method of insuring flatness of surface in a com ite sheet composed of thin wood veneer g ued to a, iexible backing and ruptured along the grain into many connected filaments, where the wood is of a, t in which bulges result from uneven s rinkage in the direction of the grain in drying from a green state, which consists in pressing the sheet at with suicient force to Hatten out the bulges and heating it to a,l

temperature in the neighborhood of the boiling-point of water and maintainingthe heat and pressure until the wood has so ned.

In testimony whereof, I sign this specifica.-

tion.

ARMIN ELMENDORF. 

